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  • Microfluidic approaches for the production of monodisperse, superparamagnetic microspheres in the low micrometer size range
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Reka Geczy, Monica Agnoletti, Mikkel F. Hansen, Jörg P. Kutter, Katayoun Saatchi, Urs O. Häfeli

    The preparation of small, monodispersed magnetic microparticles through microfluidic approaches has been consistently challenging due to the high energy input needed for droplet break-off at such small diameters. In this work, we show the microfluidic production of 1-3 μm magnetic nanoparticle-loaded poly(D, L-lactide) (PLA) microspheres. We describe the use of two approaches, using a conventional flow-focusing microfluidic geometry. The first approach is the separation of target size satellite particles from the main droplets; the second approach is the direct production using high flow rate jetting regimes. The particles were produced using a polymeric thiol-ene microfluidic chip platform, which affords the straightforward production of multiple chip copies for single-time use, due to large feature sizes and replica molding approaches. Through the encapsulation of magnetite/maghemite nanoparticles, and their characterization with scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) measurements, we show that the resulting particles are monosized, highly spherical and exhibit superparamagnetic properties. The particle size regime and their magnetic response show potential for in vivo intravenous applications of magnetic targeting with maximum magnetic response, but without blocking an organ’s capillaries.

    更新日期:2018-09-25
  • Enhanced electromagnetic wave absorption properties of NiCo2 nanoparticles interspersed with carbon nanotubes
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Bochong Wang, Can Zhang, Congpu Mu, Ruilong Yang, Jianyong Xiang, Jiefang Song, Fusheng Wen, Zhongyuan Liu

    The NiCo2 nanoparticles and NiCo2/carbon nanotubes (CNTs) nanohybrids were prepared by a single-model microwave heating and annealing treatment. It was found that the NiCo2 nanoparticles were evenly distributed around with CNTs. As a result, the complex permittivity of NiCo2/CNTs nanohybrids could be adjusted effectively, and achieved a well impedance matching for the microwave absorption. The dielectric loss, magnetic loss mechanism and the impedance matching were also investigated systematically. As a result, the reflection loss (RL) less than -20 dB (99% absorption) were observed at 3.7-16.5 GHz with the thickness of 1.2-4.0 mm; moreover, the maximum bandwidth of the RL values less than -10 dB (90% absorption) was 4.4 GHz (12.5-16.9 GHz), and a minimum RL value of -25.5 dB could be observed at 14.7 GHz with the thickness of 1.3 mm. These performances revealed that the NiCo2/10%CNTs nanohybrids have a great potential to be used as the lightweight microwave absorption material.

    更新日期:2018-09-25
  • Experimental study on fracture process of sintered Nd-Fe-B magnets during dynamic Brazilian tests
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Huanran Wang, Chunying Ren, Yin Wan, Danian Chen, Chu Guangxiang

    The deformation and fracture processes of the Nd-Fe-B magnets during dynamic Brazilian tests were investigated using a split Hopkinson pressure bar (SHPB) with a high-speed photography (HSP) and digital image correlation (DIC). The load and work applied to the specimens were determined with the strain signals of incident, reflected and transmitted wave of the SHPB tests. It was revealed with HSP and DIC that at a load time before the maximal load, some cracks along the loaded diameter on the specimen surface became visible. The localized fracture strains at representable points of the failed area were given by DIC. The tensile strength of the specimens was obtained based on the elasticity theory when the load reached the maximum. The widths of the failed area on the specimen surface at the maximal load were determined with DIC. Furthermore, the fracture work applied to the specimen per failed volume which corresponds to the maximal load was given and could be an energy criterion for the fracture of the Nd-Fe-B specimens. It was indicated that the tensile strength and fracture work of the Nd-Fe-B magnets increase with the increase of strain rate in the Brazilian tests. It was shown that the transgranular fracture became visible in the recovered specimens for the higher strain rate tests.

    更新日期:2018-09-25
  • Influence of Al doping on the magnetoresistance and transport properties of La0.7Ba0.3Mn1-xAlxO3 (0≤ x ≤0.15) manganites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Devendra K. Pandey, Anchit Modi, Kumud Dubey, Padmini Pandey, Vikash Sharma, G.S. Okram, N.K. Gaur
    更新日期:2018-09-25
  • Cyclic Structural Ordering Induced by High Energy Ball Milling in a Fe2.1Cr0.9Al Magnetocaloric Alloy
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Vinay Sharma, Shashwat Shukla, Xi Shibo, Du Yonghua, R.V. Ramanujan
    更新日期:2018-09-25
  • First-Order Reversal Curve (FORC) Diagrams of Nanomagnets with Cubic Magnetocrystalline Anisotropy: A Numerical Approach
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-25
    Miguel A. Valdez-Grijalva, Adrian R. Muxworthy

    First-order reversal curve (FORC) diagrams are increasingly used as a material’s magnetic domain state fingerprint. FORC diagrams of noninteracting dispersions of single-domain (SD) particles with uniaxial magnetocrystalline anisotropy (MCA) are well studied. However, a large class of materials possess a cubic MCA, for which the FORC diagram properties of noninteracting SD particle dispersions are less understood. A coherent rotation model was implemented to study the FORC diagram properties of noninteracting ensembles of SD particles with positive and negative MCA constants. The pattern formation mechanism is identified and related to the irreversible events the individual particles undergo. Our results support the utility of FORC diagrams for the identification of noninteracting to weakly-interacting SD particles with cubic MCA.

    更新日期:2018-09-25
  • Enhancement of Electrical and Magnetic Properties of cobalt ferrite nanoparticles by co-substitution of Li-Cd ions
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-22
    Saadia Rasheed, Rafaqat Ali Khan, Faheem Shah, Bushra Ismail, Jan Nisar, Syed Mujtaba Shah, Abdur Rahim, Abdur Rahman Khan

    A series of Li-Cd doped cobalt ferrites CoLixCdxFe2-2xO4(x= 0.05, 0.1, 0.15, 0.2, 0.25) has been synthesized by hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) as capping agent. XRD data has confirmed the formation of single crystalline cubic phase with average crystallite size of synthesized samples between 24-28nm. For all the samples the resistivity was found to increase with increase in dopants concentration with highest value of 7.3× 107ohm.cm at Li-Cd content x= 0.1. Dielectric constant values of all the samples follow the typical Maxwell-Wagner type dispersion due to interfacial polarization and were observed to decrease with increase in frequency, which is a typical phenomenon in ferrites. The coercivity (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) of all the samples increase with dopant content, with maximum values of 936 Oe, 54 emug-1 and 30 emug-1 respectively at x=0.1. The obtained data with improved coercivity, saturation magnetization and remanent magnetization make Li-Cd doped cobalt ferrites as suitable materials for utilization in transformer cores and transmission lines.

    更新日期:2018-09-25
  • Role of Tin and Carbon in the magnetic interactions in Mn3SnC
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-22
    V.N. Gaonkar, E.T. Dias, Arka Bikash Dey, Rajendra Prasad Giri, A.K. Nigam, K.R. Priolkar

    In this paper we attempt to understand the role of tin and carbon in magnetic interactions in Mn3SnC. Mn3SnC exhibits a time dependent magnetic configuration and a complex magnetic ground state with both ferromagnetic and antiferromagnetic orders. Such a magnetic state is attributed to presence of distorted Mn6C octahedra with long and short Mn–Mn bonds. Our studies show that C deficiency increases the tensile strain on the Mn6C octahedra which elongates Mn–Mn bonds and strengthens ferromagnetic interactions while Sn deficiency tends to ease out the strain resulting in shorter as well as longer Mn–Mn bond distances in comparison with stoichiometric Mn3SnC. Such a variation strengthens both, ferromagnetic and antiferromagnetic interactions. Thus the structural strain caused by both Sn and C is responsible for complex magnetic ground state of Mn3SnC.

    更新日期:2018-09-25
  • Synthesis and magnetic properties of spinel Zn1−xNixFe2O4 (0.0≤ x≤ 1.0) nanoparticles synthesized by microwave combustion method
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-22
    A. Abu El-Fadl, A.M. Hassan, M.H. Mahmoud, Tetiana Tatarchuk, I.P. Yaremiy, A.M. Gismelssed, M.A. Ahmed

    Nanoparticles of Zn1-xNixFe2O4 (x=0.0–1.0 in step of 0.2) ferrites are synthesized by microwave combustion method using glycine as a fuel. The structure, site occupancy and ferrimagnetic behavior have been characterized by X-ray diffraction (XRD), Mössbauer Spectroscopy (MS) and Vibrating Sample Magnetometer (VSM). Special emphasis is given to the information provided by each of these techniques concerning the impact of the site occupancy on the magnetic properties. The results reveal the formation of single phase cubic spinel with crystallite sizes in the range of 30-42 nm. The lattice constants and the lattice strains decrease gradually with increasing Ni-content. Two well-defined Mössbauer sextets in the spectra at 78 K belong to octahedral [B] and tetrahedral (A) sites, respectively, confirming the formation of Zn1-xNixFe2O4 spinel. The isomer shift (δFe) values were assigned to Fe3+ ions distributed in both A and B sites. The quadrupole splitting (Δ) values showed also that the orientation of the magnetic hyperfine field (Hint) with respect to the principle axes of the electric field gradient (EFG) is random. The nanosize samples In the presence of an externally applied magnetic field prepared exhibit the hysteresis loops of the ferrimagnetic nature. The value of saturation magnetization increases with introducing Ni up to x=0.8 and then it decreases. The magnetic data parameters of this structure are discussed as a function of the content of Ni ions.

    更新日期:2018-09-25
  • Unique influence of heating rate on the magnetic softness of Fe81.5Si0.5B4.5P11Cu0.5C2 nanocrystalline alloy
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-22
    Lixian Jiang, Yan Zhang, Xing Tong, Tsuyoshi Suzuki, Akihiro Makino

    Fe81.5Si0.5B4.5P11Cu0.5C2 nanocrystalline alloy with high Fe concentration possesses a finely uniform nanocrystalline structure and numerous α-Fe crystals with a mean grain size of ∼17 nm based on XRD patterns. Such crystals precipitated from the amorphous matrix. Favorable soft magnetic properties, small value of coercivity (Hc) of ∼4.8 A/m, and high magnetic flux density (Bs) of ∼1.53 T can be achieved by slow heat treatment (heating rate of ∼10 °C/min). In this case, one-step annealing at a low heating rate is truly antipodal to Fe–Si–B–P–Cu alloy. We analyzed the nanocrystallized mechanism during annealing with various heating rates in Fe81.5Si0.5B4.5P11Cu0.5C2 alloy, which inevitably simplified the industrial crystallization process by one-step annealing at a low heating rate.

    更新日期:2018-09-25
  • Electric polarization in two-layer bounded ferromagnetic film
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-22
    N.V. Shula, R.A. Doroshenko

    A numerical study of the ground state of a two-layer ferromagnetic bounded film is carried out. The film layers have uniaxial anisotropy easy-plane and easy-axis. All calculations were carried out for films with parameters of ferrites-garnets – Materials that admit a magnetoelectric effect. The ground state was calculated using a three-dimensional micromagnet modeling package OOMMF for rectangular films of different sizes. It was shown that in a film, along with a homogeneous ground state, the vortex distribution of the magnetization is realized. For the vortex distribution, the electric polarization is calculated. It was found that the component of the electric polarization vector of the film perpendicular to the film plane is nonzero. This is due to the presence of the vortex core. The change in the electric polarization due to magnetic reversal of the film by an external magnetic field is studied. It is shown that as the field increases, the polarization modulus also increases to certain field values, and then decreases to zero. As the transverse dimensions of the film decrease, the magnitude of the maximum of the electric polarization increases.

    更新日期:2018-09-25
  • Preparation of Mn-diffused Sm-Fe-N core-shell powder by reduction-diffusion process
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Masashi Matsuura, Keisuke Yarimizu, Yohei Osawa, Nobuki Tezuka, Satoshi Sugimoto, Takashi Ishikawa, Yukinobu Yoneyama

    Although the addition of other elements such as Mn to Sm2Fe17Nx compounds can change the magnetic properties, it also decreases saturation magnetization. In order to exploit the advantages of additional elements in Sm2Fe17Nx powder while maintaining a high saturation magnetization, a structure of Sm2Fe17Nx-core/Sm2(Fe,M)17Nx-shell is promising. This is the first report of such a core-shell powder obtained by a reduction-diffusion process. Mn3O4 was mixed with Sm-Fe and Sm2O3 powders followed by the reduction by Ca above 860 °C, and then samples were nitrided and washed after reduction-diffusion process. Core-shell Sm-Fe-N fine powder with a Mn-enriched Sm2(Fe,Mn)17Nx shell was thus successfully obtained. The thickness of the Mn enriched region was about 0.8 μm, and the crystal structure of the core-shell powder was Th2Zn17. The saturation magnetization and coercivity of the core-shell powder were 138.8 A⋅m2⋅kg-1 and 1001.7 kA⋅m-1, respectively. The saturation magnetization was slightly smaller than that of Mn-free Sm-Fe-N powder, whereas the coercivity of the core-shell powder was higher than that of Mn-free Sm-Fe-N powder. In addition, the saturation magnetization and coercivity were higher than those reported for Sm-Fe-Mn-N powder. The thermal stability of the Mn-diffused Sm-Fe-N core-shell powder was improved compared with Mn-free Sm-Fe-N powder.

    更新日期:2018-09-25
  • Exchange Bias and Spin Glass in La2FeMnO6 Nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    J.B. de Azevedo Filho, J.H. de Araújo, M.A. Morales, C.L. Firme, J.B. de Oliveira

    The aim of this work is to study the La2FeMnO6 double perovskite system from an experimental point of view. The nanoparticles were prepared through the ionic coordination reaction method and have a mean particle size of 36 nm, as determined by MEV analysis. The crystal structure is monoclinic with P21/n space group. The 57Fe Mössbauer spectroscopy (MS) study reveals that Fe ions species have a dominant magnetic spectra at temperatures smaller than 90 K, and above 180 K the spectra are dominated by a paramagnetic component. The magnetization versus temperature (MxT) measurement showed a fast increase of magnetization at temperatures below 130 K and seems to be related to the Fe moments. The M−1 x T data follows a linear trend for T > 591 K indicating a magnetic transition at this temperature. The MS and the magnetic data reveal that for T > 180 K the ferromagnetic signal is mainly due to Mn3+-O-Mn+4 clusters. Studies on AC susceptibility as a function of frequency suggested a cluster spin glass transition at 98.9 K, and the field cooling MxH loops depicted an exchange bias effect below 20 K. Both results indicate the complexity of this system making it of great interest in basic research and practical applications.

    更新日期:2018-09-25
  • Spin current induced dynamics and polarity switching of coupled magnetic vertices in three-layer nanopillars
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    A.E. Ekovasov, S.V. Stepanov, K.A. Zvezdin, E.G. Ekomasov

    We study dynamics of two magnetostatically coupled magnetic vortices excited by spin-polarized electrical current in a nanopillar consisting of permalloy magnetic layers with different thickness separated by a nonmagnetic spacer. We demonstrate three dynamical regimes of the vortices bound motion: damped oscillations, stationary oscillations and a regime of the polarity switching of one of the vortices; the critical currents for each dynamical phase are identified. The structure and trajectory of the vortex core motion in each magnetic layer are studied for the case of the vortex polarity switching in a thick layer. We show that the vortex polarity switching process has a dynamic nature and is associated with a vortex-antivortex pair formation.

    更新日期:2018-09-25
  • Significantly enhancing the coercivity of NdFeB magnets by ternary Pr-Al-Cu alloys diffusion and understanding the elements diffusion behavior
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Huixin Zeng, Zhongwu Liu, Wei Li, Jiasheng Zhang, Lizhong Zhao, Xichun Zhong, Hongya Yu, Baochun Guo

    Low melting point Pr-Al-Cu alloys were employed in grain boundary diffusion for sintered NdFeB magnets. The coercivity of the 7×7×2 mm magnet was enhanced from 1000 kA/m to 1360, 1615, and 1714 kA/m by diffusing Pr70Al10Cu20, Pr70Al15Cu15 and Pr70Al20Cu10 alloys, respectively, at 800°C for 2 h followed by 500°C for 3 h. The optimized microstructure with strip-like grain boundary phase was evident in diffused magnets, which helps to reduce the magnetic exchange interaction between the hard magnetic grains and improve the coercivity. Under the same diffusion process, the coercivity of the diffused magnets decreased with increasing sample thickness, but 27% coercivity enhancement can still be obtained in the magnet with 6 mm in height. A Φ10×10 mm block magnet was diffused by Pr70Al20Cu10 alloy at 800°C for 2∼10 h. Up to 49% enhancement in coercivity was achieved, which confirms the diffusion ability of Pr-Al-Cu alloy. The diffusion behavior of Pr, Al and Cu elements has been analyzed by Fick’s law. Based on the diffusion coefficients obtained at 800 and 900°C, Pr diffuses faster than Cu and Al along the grain boundary. The current results demonstrated that Pr-Al-Cu alloys can effectively optimize the grain boundary structure and improve the coercivity of NdFeB magnets.

    更新日期:2018-09-25
  • Structural, morphological, enhanced magnetic properties and antibacterial bio-medical activity of rare earth element (REE) Cerium (Ce3+) doped CoFe2O4 nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    K. Elayakumar, A. Dinesh, A. Manikandan, Murugesan Palanivelu, G. Kavitha, S. Prakash, R. Thilak Kumar, S.K. Jaganathan, A. Baykal

    In this present study, we made an attempt for the different concentration of rare earth element (REE) Cerium (Ce3+) doped cobalt ferrite (CoFe2O4) nanoparticles (NPs) were prepared by the simple sol-gel combustion technique. Cerium was successfully substituted into the spinel lattice without any distortion. It was analyzed the effect of Ce3+ ions doping on structural, morphological, magnetic properties and antibacterial activities using the various instrument techniques. Powder XRD and SEM along with EDX studies confirmed the pure phase formation Ce3+ doped CoFe2O4 NPs and spherical shaped agglomerated nanoparticles morphology without any other impurity. The well resolved broad peaks in the XRD pattern clearly indicated the nanosized, single phased, cubic spinal nature of these samples. There was a substantial decrease in the crystallite size on doping with Ce3+. A more in-depth morphological study was facilitated using the TEM and SAED analysis. TEM investigation revealed random shaped, sharp edged nanoparticles with a normally facetted morphology. The presence of distinctive diffractions spots on the SAED pattern indicated the formation of nanoparticles that are highly crystalline in nature. The magnetic response of the Ce3+ doped CoFe2O4 NPs was recorded at room temperature (RT) using the VSM technique. The magnetic properties have been seen to be altered by the addition of Ce3+ in the CoFe2O4 matrix. The decrease in the saturation magnetization (Ms, emu/g) with the increase in Ce3+ content rendered the synthesized sample applicable in field of antenna construction. This change will be also suitable for reducing the size of the antenna. The antibacterial activity of Ce3+ doped CoFe2O4 nanoparticles was found to be enhanced with increase in Ce3+ doping level as it cause a reduction in the grain size.

    更新日期:2018-09-25
  • Coercivity enhancement of hot-pressed magnet prepared by HDDR Nd–Fe–B powders using Pr-Cu eutectic alloys diffusion
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Tingting Song, Xu Tang, Wenzong Yin, Renjie Chen, Aru Yan

    The effect on the Nd-rich phase distribution of the ingot for hydrogenation-disproportionation-desorption-recombination (HDDR) powders was studied. Coercivity of HDDR powders was elevated to 1.64 T by crushing the ingot into particles and annealing at 800 °C for 18 h. HDDR processed Nd-Fe-B powders blended with Pr-Cu powders and annealed at 580 °C for 3 h were hot-pressed to obtain fully dense magnets. The microstructure evolution in hot-pressed HDDR magnets proved the impact of Pr-Cu diffusion on coercivity that the coercivity of hot-pressed magnets was improved to 1.55 T significantly. Backscatter electron microscopy and transmission electron microscopy observations revealed that the variation in coercivity owing to the diffusion of Pr-Cu along the grain boundary with heat treatment. L-TEM images illustrated the thicker grain boundary layer can pin the motion of the domain wall more effectively, resulting in a higher coercivity in HP magnets.

    更新日期:2018-09-25
  • Magnetic properties of (1-x)Bi0.5Na0.5TiO3+xMnTiO3 materials
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Man Minh Hue, Nguyen Quoc Dung, Luong Thi Kim Phuong, Nguyen Ngoc Trung, Nguyen Van Duc, Luong Huu Bac, Dang Duc Dung

    MnTiO3-doped Bi0.5Na0.5TiO3 materials were fabricated by sol–gel technique. According to X-ray diffraction and Raman scattering analyses, MnTiO3 was suitable to be used as solid solution in Bi0.5Na0.5TiO3 but resulted in distorted structure. The optical band gaps decreased from 3.06 eV for pure Bi0.5Na0.5TiO3 to 1.69 eV for 9 mol% MnTiO3 solid solution in Bi0.5Na0.5TiO3. The magnetic properties of Bi0.5Na0.5TiO3 materials were tuned from ferromagnetism to combination of ferromagnetism and paramagnetic-like property with varying MnTiO3 concentration. The reduction of the optical band gap and the tunable magnetic properties of Bi0.5Na0.5TiO3 materials were due to the random distribution of Mn cation in the host lattice as a function of MnTiO3 amounts. This work provides a new trend of selecting dopants to induce ferromagnetism in lead-free ferroelectric materials.

    更新日期:2018-09-25
  • Microstructure and Coercivity in Alnico 9
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Lin Zhou, Emma White, Liqin Ke, David A. Cullen, Ping Lu, S. Constantinides, R.W. McCallum, I.E. Anderson, M.J. Kramer

    Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α1) phase embedded in continuous non-magnetic AlNi-rich (α2) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a “mosaic structure”, composed of rod-shape α1 phase with {110} or {100} planar faceting and diameter of ∼30-45nm. There is also a Cu-enriched phase residing at the corners of two <110> facets of the α1 phase. It was observed that grain boundary phase reverse magnetization direction at lower external magnetic field compared to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α1 rods, as well as their diameter, are promising routes to improve energy product of alnico.

    更新日期:2018-09-25
  • Enhanced coercivity in non-equiatomic CoPt-Cu nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    Prakash Karipoth, R. Justin Joseyphus

    Co30Cu10Pt60 nanoparticles were prepared by a simplified polyol process devoid of any surfactants or capping agents. Thermo-magnetic analysis showed that the addition of 10 at. % Cu reduces the Curie temperature of Co40Pt60 from 492 oC to 435 oC. The incorporation of Cu is effective in reducing the threshold ordering temperature for the A1-fcc to L10-fct phase transformation resulting in coercivity enhancement. Coercivity close to 10 kOe at a lower annealing temperature of 600 oC in Co30Cu10Pt60 demonstrates that high coercivity in CoPt can be achieved in non-equiatomic compositions also. Annealing temperature dependent two phase behavior has been understood by δM studies.

    更新日期:2018-09-25
  • Magnetic ordering in the nano-laminar ternary Mn2AlB2 using neutron and X - ray diffraction
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-24
    D. Potashnikov, E.N. Caspi, A. Pesach, A. Hoser, S. Kota, L. Verger, M.W. Barsoum, I. Felner, A. Keren, O. Rivin
    更新日期:2018-09-25
  • Nature of magnetoelectric coupling in corundum antiferromagnet Co4Ta2O9
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-21
    S. Chaudhary, P. Srivastava, S.D. Kaushik, V. Siruguri, S. Patnaik

    We study magnetocapacitance (MC) effect and magnetoelectric (ME) coupling in spin-flop driven antiferromagnet Co4Ta2O9. Powder neutron diffraction data reveal that the magnetic structure corresponds to a non-collinear arrangement along with a non-centrosymmetric crystal structure below Néel Temperature. Electric polarization is achieved below Néel temperature only when the sample is cooled in the presence of external magnetic field. The magnetocapacitance data at high magnetic fields are analyzed by phenomenological Ginzburg-landau theory of ferro-electromagnets and it is found that change in dielectric constant is proportional to the square of magnetization. The saturation polarization and magnetoelectric coupling are estimated to be 52µC/m2 and γ = 1.4 x10-3 (emu/g)-2 respectively at 6 Tesla. Strong magnetoelectric coupling and ferroelectric phase in the anti-ferromagnetic Co4Ta2O9 are correlated to magnetic structure as derived from neutron diffraction data.

    更新日期:2018-09-22
  • Improvement of soft magnetic properties for distinctly high Fe content amorphous alloys via longitudinal magnetic field annealing
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-21
    Hu Li, Aina He, Anding Wang, Lei Xie, Qiang Li, Chengliang Zhao, Guoyang Zhang, Pingbo Chen

    The effects of longitudinal magnetic field annealing on soft-magnetic properties (SMPs) and magnetic domain structure of Fe(82.6-85.7)Si(2-4.9)B(9.2-11.2)P(1.5-2.7)C0.8 amorphous alloys with a distinctly high Fe content of 93.5-95.5 wt.% for high Bs were investigated. It was found that longitudinal magnetic field annealing could improve soft-magnetic properties (SMPs) of amorphous alloys effectively, except the one with poor thermal stability. Superb magnetic properties containing a minimum coercivity of 0.8 A/m, a maximum effective permeability of 11×103 at 1 kHz and minimum core loss of 0.052 W/kg (at Bm = 0.9 T and f = 50 Hz) were successfully obtained. Domain structures were characterized with a Magneto-optical Kerr Microscope to unveil the mechanism of SMPs improvement. Stripe domains were observed in the annealed high Fe content amorphous alloy ribbons with optimal soft magnetic properties.

    更新日期:2018-09-22
  • Bifunctional sodium tartrate as stabilizer and reductant for the facile synthesis of Fe3O4/Ag nanocomposites with catalytic activity
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-21
    Yan Xing, Fan-Fan Ma, Ming-Li Peng, Xiang-rong Ma, Ya Zhang, Ya-Li Cui
    更新日期:2018-09-21
  • Progress with insulating nanocomposites based on ferrite plating of Sm2Fe17N3 micropowders
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-20
    N. Imaoka, E. Kakimoto, K. Takagi, K. Ozaki, M. Tada, T. Nakagawa, M. Abe

    Typical exchange spring magnets are composed of two phases, a rare-earth hard magnetic material and a metallic soft magnetic material, whose magnetization value is higher than those of hard magnetic phases, such as α-Fe, Fe-B, or Fe-Co. A novel high-electrical-resistance composite magnet was fabricated by consolidating micron-sized ferromagnetic nitride Sm2Fe17N3 powder particles coated with a continuous nano-sized soft magnetic ferrite oxide layer, which suppressed intergrain conductivity but sustained the magnetic exchange interactions between grains [J. Appl. Phys., 103 (7), 07E129-1-3, 2008]. A non-magnetic resin or ceramic insulator may suffice for the coated layer but gives rise to high electrical resistance of the magnet with large deterioration of magnetization. The soft magnetic ferrite oxide layer not only suppressed intergrain conductivity, but also only slightly reduced the magnetization of the magnet. At present, the only exchange spring magnet having a combination of a soft magnetic oxide and hard magnetic nitride is the ferrite/Sm2Fe17N3 composite magnet. Sm2Fe17N3 powder particles with a size of 2 μm were coated with an “iron ferrite” layer with a grain size of about 10 nm by ferrite plating, which is an aqueous process, following which the samples were consolidated by the explosive consolidation (EC) technique. The coercivity and rectangularity of the ferrite/Sm2Fe17N3 composite magnet decreased slightly compared to those of a Sm2Fe17N3 magnet. The fully dense ferrite/Sm2Fe17N3 magnet exhibited a resistivity of about 4000 μΩ cm, which is ten times larger than that of a fully dense Sm2Fe17N3 magnet. Thus, the soft magnetic ferrite layer in the composite magnet maintained the magnetic exchange coupling between ferromagnetic Sm2Fe17N3 grains and simultaneously suppressed intergrain electrical coupling to increase the resistivity. This decreased the eddy current loss and improved the high-frequency characteristics of the composite magnets. Therefore, ferrite/Sm2Fe17N3 composites are promising materials for magnets that are operated at high frequencies in advanced applications, such as electric vehicle magnets.

    更新日期:2018-09-21
  • Magnetic properties of Zn-substituted Y-type hexaferrites, Ba2ZnxFe2-xFe12O22
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-19
    Jae-Hyoung You, Sang-Im Yoo

    We report the magnetic properties of Zn-substituted barium Y-type hexaferrites with the Zn substituent, x, ranging from 0.5 to 2.0 in Ba2ZnxFe2-xFe12O22. After high-temperature annealing and subsequent furnace-cooling, single-phase samples with x = 0.5, 1.0, 1.5 could be successfully prepared in a reduced oxygen atmosphere (PO2 = 10-3 atm) while the single-phase was obtainable only from the sample with x = 2.0 in air. With increasing x from 0.5 to 2.0, both a lattice parameters (≈ 0.32%) and unit cell volumes (Vcell) (≈ 0.51%) were linearly increased but c lattice parameters (≈ 0.12%) were linearly decreased, which is in good agreement with the Vegard’s law, indirectly supporting a successful formation of Ba2ZnxFe2-xFe12O22-type solid solutions. The saturation magnetization (Ms) was first increased with increasing x from 0.5 to 1.0 and then decreased up to x = 2.0. Thus, the highest Ms value of 44.7 emu/g was obtainable from the sample of x = 1.0 sintered at 1300˚C for 2 h in the low PO2 of 10-3 atm. These results are attributable to the site preference of Zn2+ ions for the tetrahedral sites of Y-type hexaferrites.

    更新日期:2018-09-20
  • Effect of sputtering conditions on the structure and magnetic properties of self-assembled BiFeO3-CoFe2O4 nanocomposite thin films
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-19
    Tae Cheol Kim, Seung Han Lee, Hyun Kyu Jung, Young Eun Kim, Jun Woo Choi, Daejin Yang, Dong Hun Kim

    This article describes the growth of self-assembled spinel-perovskite nanocomposite thin films using a sputtering technique. We explore the effects of annealing and sputtering conditions such as working pressure, Ar:O2 ratio, and sputtering power on the structure, morphology, and magnetic properties of BiFeO3-CoFe2O4 nanocomposite thin films. Vertically aligned nanocomposites, consisting of CoFe2O4 grown as pillars in a BiFeO3 matrix, were observed under optimum growth conditions. The magnetic hysteresis loops of these nanocomposites showed a strong out-of-plane anisotropy originating from shape anisotropy of the pillars and magnetoelastic anisotropy of the CoFe2O4, but the latter was dominant. The physical properties of these nanocomposites were dramatically changed by modulating the growth conditions, which affected the growth rates and strain states. Finally, we provide a mapping that summarizes the structure and magnetic anisotropy changes that occur with growth rate, for optimizing synthesis conditions for self-assembled oxide nanostructures.

    更新日期:2018-09-20
  • Enhanced Microwave Absorption of Barium Cobalt Hexaferrite Composite with Improved Bandwidth via c-Plane Alignment
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-19
    Guoke Wei, Tao Wang, Hang Zhang, Xiaotong Liu, Yinlong Han, Yanchun Chang, Liang Qiao, Fashen Li

    Planar hexaferrite BaCo2Fe16O27 was prepared by a simple adsorbent combustion method. The BaCo2Fe16O27/paraffin composite with 45 vol.% particles was subjected to a rotational orientation process in an external magnetic field, resulting in highly-oriented BaCo2Fe16O27 composite with an alignment degree of 0.88. The oriented composite showed higher permeability in both real and imaginary parts as compared to its random counterpart. Significant enhancement of microwave absorbing performance was obtained for the oriented composite in 8 ∼ 18 GHz due to the enhanced impedance matching and magnetic loss, displaying much stronger absorption and greater bandwidth (≤ -10 dB) than the random composite. Moreover, a thinner matching thickness can be achieved for a given matching frequency through the alignment of easy magnetization planes. The results showed that the c-plane alignment process holds promises for rational design of lightweight magnetic absorbers with planar anisotropy.

    更新日期:2018-09-20
  • A study on the magnetocaloric effect in Ti doped manganites Gd0.7Sr0.3Mn1-xTixO3(x=0,0.1 and 0.15)
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-19
    Anitha Anand, R. K.Veena, M. Manjuladevi, V.S. Veena, Yuri S. Koshkid'ko, S. Sagar

    This work focuses on Magnetic and magnetocaloric properties of doped Gd based manganites; Gd0.7Sr0.3Mn1-xTixO3(x=0,0.1,0.15) denoted by G,G0.1,G0.15 respectively. Isothermal magnetic entropy change (|ΔS(T) |) shows appreciably high values for the three compounds. For 10T field, the peak values obtained for magnetic entropy change is 10.4JKg-1 K-1, 9.6JKg-1 K-1and 22.2JKg-1 K-1respectively for samples G,G0.1,G0.15 at 12.5K. Interestingly,-ΔS(T) shows a universal behaviour near the transition region at the low temperature. Relative cooling power (RCP) is comparatively high for Gd0.7Sr0.3Mn0.85Ti0.15O3 at low fields, but for high fields Gd0.7Sr0.3MnO3 has comparatively high values for RCP.

    更新日期:2018-09-20
  • Oguchi’s Method and Random Interaction Fields’ Method: Investigation of Properties of Ferromagnetic Materials
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-19
    V. Belokon, A. Trofimov, O. Dyachenko

    The Curie point of a ferromagnetic material is determined in the framework of the Ising model by Oguchi’s method and the random interaction fields’ method. The heat capacity of the system is also investigated. The jump in the heat capacity is calculated at the Curie point. Comparison with known results is made.

    更新日期:2018-09-20
  • New Method to Calculate Mössbauer Recoilless f-Factors in NiFe2O4. Magnetic, Morphological and Structural Properties
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-20
    H. Salazar-Tamayo, K.E. García, C.A. Barrero

    Mössbauer spectroscopy has long been used to calculate the degree of inversion (λ) in ferrites. To perform this calculation in NiFe2O4, it is assumed that the recoilless f-factors ratio of the Fe3+ cations at octahedral [B] and tetrahedral (A) sites of the spinel structure, fFeB3+fFeA3+, is equal to 1 at very low temperatures and equal to 0.94 at room temperature (RT). However, these values were reported for ideal Fe3O4 but not for NiFe2O4, and the physical properties of both materials are very different. In this work, we use a simple method and propose equations for directly determining the fFeA3+ and fFeB3+values at RT relative to the recoilless f-factor of standard metallic iron powder (fFe). NiFe2O4 was synthesized from a stoichiometric mixture of nickel oxide and hematite by combining milling processes and heat treatments. The sample was characterized using X-ray diffraction, Mössbauer spectroscopy, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and magnetic measurements. The results of all the characterization techniques confirm the synthesis of NiFe2O4 and the formation of the spinel structure. The lattice parameter of the cubic unit cell of NiFe2O4 was calculated using a crystallographic model and the Rietveld refinement. By comparing the lattice parameters, it was possible to determine the degree of inversion (λ= 0.96) of the spinel structure of NiFe2O4, and it could be established that the sample obtained has a mixed spinel structure of the type Ni0.042+Fe0.963+ANi0.962+Fe1.043+BO42-. Finally, a value of fFeB3+fFeA3+= 1.09±0.01 was calculated for NiFe2O4 at RT.

    更新日期:2018-09-20
  • Investigations of surface spin canting in Ni-Zn nanoferrite and its development as magnetic core for microwave applications
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-18
    A. Mahesh Kumar, K. Srinivasa Rao, M. Chaitanya Varma, K.H. Rao

    Nanoparticles of nickel zinc ferrite Ni0.65Zn0.35Fe2O4 having an average crystallite size of 42 nm, synthesized by sol-gel method were found to exhibit the highest value of saturation magnetization along with high dc resistivity. The observed variations in saturation magnetization and crystallite size as a function of annealing temperature were elucidated considering the core surface magnetic interactions and the particle shape of the nanoferrite using low temperature in-field Mössbauer measurements and the high-resolution transmission electron micrographs. With the attainment of valuable magnetization and resistivity, the usefulness of the material as magnetic core for high frequency applications has been investigated by studying the frequency dependence of initial permeability. Interestingly, the results support that the material would be suitable as magnetic core up to 18 GHz.

    更新日期:2018-09-19
  • Effects of applying tensile stress at the annealing temperature during annealing on the GMI and induced anisotropy of Fe-Cu-Nb-Si-B alloys
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-18
    Raymond Kwesi Nutor, Xiaojia Xu, Xiaozhen Fan, Xingwei He, Xuanan Lu, Yunzhang Fang

    Nanocrystalline Fe73.5Cu1Nb3Si13.5B9 ribbon samples possess excellent soft magnetic properties. Three forms of annealing treatment were performed on amorphous Fe-Cu-Nb-Si-B ribbon samples. The microstructure of the ribbon samples is studied using synchrotron radiation XRD. It is seen that upon annealing, a microstructure of nanocrystalline phase embedded in a residual amorphous matrix is achieved. The application of tensile stress (i) at the annealing temperature till cooling down to room temperature and (ii) from room temperature throughout the annealing process till cooling down to room temperature both show a clear difference in the XRD peaks in the directions parallel and perpendicular to the ribbon directions indicative of an induced structural anisotropy. The transition from the amorphous phase to the nanocrystalline phase was also confirmed by the GMI and transverse field anisotropy measurements. The application of tensile stress at the annealing temperature induces an anisotropy similar to the conventional stress annealing process, with about 5% less strain. This could be a method of reducing the brittle fracture problem of nanocrystalline ribbon samples.

    更新日期:2018-09-19
  • Laminar ferrofluid heat transfer in presence of non-uniform magnetic field in a channel with sinusoidal wall: a numerical study
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-18
    Ali Asadi, Alireza Hossein Nezhad, Faramarz Sarhaddi, Tahereh Keykha

    This research is allocated to numerical study of two dimensional laminar forced convective heat transfer of ferrofluid (water and Fe3O4) in the presence of a non-uniform magnetic field in a channel with a sinusoidal corrugated wall. The hydrodynamic and thermal behavior of the ferrofluid is examined using the mixture model and the finite volume method. The effects of an increase in wavy channel amplitude, volume fraction, Reynolds number, and negative magnetic field gradient on the hydrodynamic and thermal behaviors are investigated and discussed. Nusselt number is found to increase as wave amplitude, volume fraction of nanoparticles, Reynolds number, or negative magnetic field gradient increase. The negative magnetic field gradient increases the pump work with a greater effect at lower Reynolds numbers. The results of this research can be utilized to enhance heat transfer in heat exchangers and to increase their efficiency.

    更新日期:2018-09-18
  • Cold plasma reduction of surface carbon on SmCo5 nano-flakes prepared by surfactant-assisted ball-milling
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-17
    Guangbing Han, Ke Wang, Kevin E. Elkins, Zhaoguo Qiu, Richard B. Timmons, Charles R. Savage, Shishou Kang, J. Ping Liu

    Nano-flake SmCo5 powders with typical flake thickness of 200 nm were prepared by high energy ball milling using Oleic Acid (OA) as a surfactant. In order to remove the surfactant, the as-milled powders were exposed to pulse cold plasma of argon. The effects of the plasma parameters on residual surfactant content and magnetic properties of the resulting powder were investigated. Partial (62.5 at. %) surfactant removal was observed by XPS after treatments of 4 hrs at 150 Watt average power under an argon pressure of 300 mTorr. In addition, the cold plasma cleaning process led to a little bit of increase of oxygen on the surface. Demagnetization measurements revealed a slight decrease of the magnetic performance after plasma treatment. These results indicate that pulse cold plasma is an effective way for surfactant removal without morphological change and magnetic property degradation of the SmCo5 nano-flakes.

    更新日期:2018-09-18
  • Magnetic interaction in a 2D solid through hydrogen bonds and π-π stacking
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-17
    M.M. González, H. Osiry, M. Martínez, J. Rodríguez-Hernández, A.A. Lemus-Santana, E. Reguera
    更新日期:2018-09-18
  • Design of high resistivity light-rare-earth-based PrFe1.93 magnetostrictive alloys: Si doping and high-pressure annealing
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-17
    Z. Zhang, W.J. Lu, S.Z. Dong, H.R. Bai, T.N. Yang, D.H. Wei, J.J. Ni, W. Li, C.C. Hu, Y.G. Shi, H.Y. Li, J.G. Hao, P. Fu, W.F. Rao

    Light-rare-earth-based Pr(Fe1-xSix)1.93 alloys (0⩽x⩽0.1) with pure cubic Laves phase were synthesized by high-pressure annealing method. Si substitution effects on magnetic, electrical and magnetostrictive properties of light-rare-earth-based Pr(Fe1-xSix)1.93 alloys were systematically investigated. It was found that the lattice parameter a and Curie temperature TC of the cubic Laves phase in the alloys increase with the increasing Si content up to x=0.05, which might be ascribed to the preferential occupation of Si in the Laves phase interstitial sites. The magnetization at the maximum available field of 15 kOe, σ15k, decreases monotonically with the increasing x. A significant increase of 67% in electrical resistivity was observed in Pr(Fe0.9Si0.1)1.93 alloy at room temperature. The magnetostriction at the field of 3 kOe of Pr(Fe0.95Si0.05)1.93 is about 542 ppm, which is even larger than the saturation magnetostriction of heavy-rare-earth-based Tb0.2Dy0.22Ho0.58Fe2 single crystal (λs=530 ppm). The attractive price, lower eddy current loss, together with high magnetostrictive response suggest that the Pr(Fe0.95Si0.05)1.93 alloy might be a good candidate material for the potential magnetostrictive applications.

    更新日期:2018-09-18
  • Investigation of the magnetic and magnetocaloric properties in metamagnetic REFe2Si2 (RE= Pr and Nd) compounds
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-17
    Yihui Ma, Xiaoshi Dong, Yang Qi, Lingwei Li

    The crystal structure, cryogenic magnetic and magnetocaloric properties in NdFe2Si2 and PrFe2Si2 compounds have been investigated. The NdFe2Si2 and PrFe2Si2 crystallized in the body-centered tetragonal structure with the space group of I4/mmm, and underwent first order magnetic transition from paramagnetic to antiferromagnetic (PM - AFM) around Néel temperatures TN of 8.5 K and 15.5 K, respectively. Under an applied-field change of ΔH=5 T, the maximum values of magnetic entropy change (-ΔSMmax) are 6.4 J/kg·K and 12.4 J/kg·K for PrFe2Si2 and NdFe2Si2, corresponding to relative cooling power (RCP) values of 0.8 J/cm3 and 1.0 J/cm3, respectively. Moreover, under low applied field change and at low temperatures, the PrFe2Si2 and NdFe2Si2 show an inverse MCE because of the existence of the AFM ordering, while under high external magnetic field change, a normal reversible MCE is observed, which is caused by first-order magnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) state.

    更新日期:2018-09-17
  • Microstructural and magnetic investigation of vanadium-substituted Sr-nanohexaferrite
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-15
    M.A. Almessiere, Y. Slimani, H.S. El Sayed, A. Baykal, I. Ercan

    In the present study, the preparation of nanocrystalline strontium vanadium nanohexaferrites was undertaken using a sol-gel auto-combustion method. The structural and morphological properties were characterized using X-ray diffraction (XRD), Fourier transform infra-red (FT-IR) analysis, and scanning electron microscopy (SEM). The XRD analysis showed that the crystallite sizes (t) of the products vary between 55 and 60 nm, while the SEM analysis confirmed the hexagonal platelet structure of the products. The magnetic hysteresis loops indicated that the synthesized nanohexaferrites exhibit ferrimagnetic-like (FM) behavior. The deduced saturation (MS) and the remnant (Mr) magnetizations, the coercive (HC) and magneto-crystalline anisotropy (Ha) fields diminished as the V3+ content increased. The Ha values are very high, pointing to the hard FM characteristics of the synthesized nanohexaferrites. Except for x=0.0, the squareness ratios, Mr/MS, are below 0.50, suggesting the presence of multi-domain nano-sized particles for SrFe12-xVxO19 (0.00 ≤ x ≤ 0.1) nanohexaferrites.

    更新日期:2018-09-17
  • 更新日期:2018-09-17
  • An Isoparametric Approach to Model Ferromagnetic Hysteresis Including Anisotropy and Symmetric Minor Loops
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-14
    B. Sai Ram, S.V. Kulkarni

    Modelling hysteresis behaviour is an essential task in transient analysis of electrical machines. A curve fitting approach based on isoparametric elements is proposed in this work. A hysteresis loop is split into sub-curves and each sub-curve has been modelled in terms of a second degree polynomial using three data points. Thus the model requires few data points to model a complete loop. The model equations can be easily derived using predefined shape functions of an isoparametric element without using any curve fitting algorithms. The proposed approach has been applied to model hysteresis data of two different materials, namely, grain-oriented (GO) laminations and soft magnetic composites (SMC). Symmetrical minor loops of GO materials with magnetization along any arbitrary direction are modelled for the first time. The calculated results are in close agreement with measured values. Compared to existing methods, the proposed technique in this paper is simple to understand and computationally efficient.

    更新日期:2018-09-15
  • Prediction of possible martensitic transformations in all-d-metal Zinc-based Heusler alloys from first-principles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-15
    Yinlin Han, A. Bouhemadou, R. Khenata, Zhenxiang Cheng, Tie Yang, Xiaotian Wang

    Several newly designed Zinc-based all-d-metal Heusler alloys have been predicted, and their XA- and L21-type atomic-site preferences, electronic structures, magnetic properties, as well as their possible martensitic phase transformations, have been studied theoretically from first principles. For cubic-type Zn2MMn (M = Ru, Rh, Pd, Os, Ir) alloys, their L21-type phase is more stable than the XA phase, that is, the two Zn atoms prefer to locate at the A (0,0,0) and C (0.5, 0.5, 0.5) positions in the lattice. Their magnetic state is ferromagnetic (FM), with a large total magnetic moment (>3 µB/f.u), and the total magnetic moment arises mainly from the Mn atom due to its strong exchange splitting. Remarkably, Zn2MMn alloys with a tetragonal martensitic structure can lower their total energies and show more stable behaviour than cubic systems. The energy difference ΔEM is defined as the difference in total energy between the martensitic and cubic states. Δ EM can be tuned under uniform strain, namely, as the lattice constant increases, Δ EM also increases. Moreover, in the case of martensitic-type Zn2RuMn and Zn2OsMn alloys, quite large c/a ratios (1.41, 1.43, respectively) can be found, which is preferable for the transformation strain effect. It is hoped that this work can motivate researchers to look for new spintronic and magnetic-intelligent materials among all-d-metal Heusler alloys.

    更新日期:2018-09-15
  • 更新日期:2018-09-14
  • Domain Wall Characterization Inside Grain and Around Grain Boundary under Tensile Stress
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-12
    Jia Liu, Gui Yun Tian, Bin Gao, Kun Zeng, Fasheng Qiu

    Stress measurement is important field of Non-destructive testing and evaluation (NDT&E). This can ensure the stability and structural rigidity of the workpiece. The challenging task of stress measurement is the properties characterization of the microscopic magnetic, especially the microstructure at different location of grains. The qualitative analysis of magnetic properties changes under low stresses inside grain and around grain boundary are difficult to obtain a reliable solution. This paper investigates characters of the domain wall inside grains and around grains boundaries under low tensile stresses. The domain wall of the silicon steel sheet is captured by the magneto-optical Kerr effect (MOKE) microscopy. The stress changes the magneto-elastic energy and the angle between magnetization and stress. The relationship among domain wall, magneto-elastic energy, the magnetization inside grains and around grains boundaries under different tensile stresses is provided and analyzed in details. Magnetization work calculates the energy required for magnetization to quantify the difference of the magnetic domains distribution caused by increment of magneto-elastic energy under different tensile stresses in different locations. The difference of magnetization work in these locations is highly affected by the tensile stress. This proposed work has the potential to evaluate the effect of grain and grain boundary on stress measurement.

    更新日期:2018-09-13
  • Can the correspondence principle lead to improper relations between the uniaxial magnetic anisotropy constant K and the axial zero-field splitting parameter D for adatoms on surfaces?
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-13
    Czesław Rudowicz, Krzysztof Tadyszak, Tomasz Ślusarski

    Studies of magnetic adatoms on surfaces utilize experimental techniques (scanning tunneling microscopy (STM), inelastic tunneling spectroscopy (ITS)) and ab-initio modeling methods. Several fundamental issues involved in these studies, being of utmost importance in view of potential technological applications, are critically examined and elucidated. This includes applications of the correspondence principle and relationships between the notions: magnetic anisotropy (MA), magnetic anisotropy energy (MAE), single-ion anisotropy (SIA), zero-field splitting (ZFS) as well as spin-flip energy of tunneling electrons and energy barrier to magnetization reversal. Proper quantum-mechanical relations between the uniaxial SIA constant K and the axial ZFS parameter D valid for the cases D > 0 and D < 0, as well as integer and half-integer spins, including S = 1/2, are derived. These considerations show that direct equating SIA with ZFS is unwarranted, whereas usage of the correspondence principle to justify such equating proves redundant. So-derived improper relations bear detrimentally on interpretation of STM/ITS and ab-initio results, e.g. for Co(S = 1) and Fe(S = 3/2) on Pt(111) yielding K (aka 'MAE') values differing from those obtained from the proper relations by 100 and 50 percent, respectively. Implications of confusion concerning the basic tenets for S = 1/2 systems, classical versus quantum spin approaches, and applicability of the crucial notions for magnetic adatoms are also discussed.

    更新日期:2018-09-13
  • Insights on the Design of a Novel Multicomponent Microwave Absorber Based on SrFe10Al2O19 and Ni0.5Zn0.5Fe2O4/MWCNTs/polypyrrole
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-12
    Mojtaba Jafarian, Seyyed Salman Seyyed Afghahi, Yomen Atassi, Mohsen Salehi

    We present the preparation of a novel microwave absorber based on a combination of two ternary composites of SrFe10Al2O19/MWCNTs/polypyrrole and Ni0.5Zn0.5Fe2O4/MWCNTs/polypyrrole. The hard and soft ferrites are prepared using the combustion method, while the polymer is deposited by in-situ polymerization method on the ferritic core. X-ray diffractometer (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and vector network analysis (VNA) are used to perform microstructural, magnetic and electromagnetic characterization of the nanocomposite. The composite sown in polyester resin exhibits a minimum reflection loss of -34.5 dB at a matching thickness of 3 mm and with a bandwidth of 3.05 GHz. The results also indicate that the total EMI shielding SET in the current composite is mainly due to the contribution of the absorption component (SEA) rather than the reflection one (SER).

    更新日期:2018-09-12
  • Anomalous ferromagnetic behavior and size effects in CuO nanowires
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-12
    A. Zúñiga, L. Fonseca, J.A. Souza, C. Rivaldo-Gomez, C. Díaz Pomar, D. Criado
    更新日期:2018-09-12
  • Alternating Magnetic Force Microscopy: effect of Si doping on the temporal performance degradation of amorphous FeCoB magnetic tips
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-11
    M.V. Makarova, Y. Akaishi, T. Ikarashi, K.S. Rao, S. Yoshimura, H. Saito

    In order to increase the resolution of traditional MFM and extend its applications in the past, we created an Alternating Magnetic Force Microscopy (A–MFM) with a magnetic force modulation by applying an off-resonance AC magnetic field. A new magnetic tip has been developed for A–MFM in this work. Perpendicular magnetic recording medium with 500 kfci recording density is successfully imaged and analyzed by using the new tips coated by 6–15 nm amorphous FeCoSiB-based soft magnetic film. The effect of Si doping to the magnetic film on the A–MFM imaging was studied. It was found that Si additive had no effect on the imaging properties, such as signal–to–noise ratio and spatial resolution (kept at ∼5 nm level). But on other side, Si additive significantly degraded the chemical stability of FeCoSiB film due to oxidation in ambient atmosphere. Surface passivation by metal and boron oxides is considered to have a main effect on improvement of chemical stability of Si–free magnetic coating. The results have shown that Si–free FeCoB-based magnetic tips are appropriate candidates for A-MFM imaging in ambient conditions.

    更新日期:2018-09-11
  • Magnonic heat transport in the Lieb lattice
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-11
    P.T.T. Le, Mohsen Yarmohammadi

    In this article we report the effect of charged impurity doping on the thermal spin-wave excitations of 2D Lieb lattice using the longitudinal/transverse and in-plane magnonic heat transport properties in a systematically Green’s function approach and the Born approximation. We present numerical results for XY Heisenberg model. Accordingly, the flow of magnonic current is enhanced depending on the impurity concentration, in which (i) at very low and very high concentrations, in-plane magnon conductivity becomes negative, (ii) the magnon Seebeck coefficient decreases (increases) before (after) a critical impurity concentration for both longitudinal/transverse and in-plane components, (iii) the longitudinal/transverse magnon thermal conductivity increases slightly with impurity concentration, while the in-plane one becomes flat, and (iv) both longitudinal/transverse and in-plane magnonic heat transport efficiencies decrease (increase) at low (high) temperatures with low impurity concentrations, whereas become flat (decrease) at high impurity concentrations. Our results are useful for the implementation of a new spin energy conversion and capable spin-filter devices for the spintronic community.

    更新日期:2018-09-11
  • Anomalous spin frustration enforced by a magnetoelastic coupling in the mixed-spin Ising model on decorated planar lattices
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-11
    Jozef Strečka, Matúš Rebič, Onofre Rojas, Sergio Martins de Souza

    The mixed spin-1/2 and spin-S Ising model on a decorated planar lattice accounting for lattice vibrations of decorating atoms is treated by making use of the canonical coordinate transformation, the decoration-iteration transformation, and the harmonic approximation. It is shown that the magnetoelastic coupling gives rise to an effective single-ion anisotropy and three-site four-spin interaction, which are responsible for the anomalous spin frustration of the decorating spins in virtue of a competition with the equilibrium nearest-neighbor exchange interaction between the nodal and decorating spins. The ground-state and finite-temperature phase diagrams are constructed for the particular case of the mixed spin-1/2 and spin-1 Ising model on a decorated square lattice for which thermal dependencies of the spontaneous magnetization and specific heat are also examined in detail. It is evidenced that a sufficiently strong magnetoelastic coupling leads to a peculiar coexistence of the antiferromagnetic long-range order of the nodal spins with the disorder of the decorating spins within the frustrated antiferromagnetic phase, which may also exhibit double reentrant phase transitions. The investigated model displays a variety of temperature dependencies of the total specific heat, which may involve in its magnetic part one or two logarithmic divergences apart from one or two additional round maxima superimposed on a standard thermal dependence of the lattice part of the specific heat.

    更新日期:2018-09-11
  • Spin-Hamiltonian parameters and zero-field splitting of impurity Gd3+ ions in SrY2O4 crystal
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-11
    B.F. Gabbasov, D.G. Zverev, I.F. Gilmutdinov, R.G. Batulin, A.G. Kiiamov, S.I. Nikitin, R.V. Yusupov

    Electron paramagnetic resonance (EPR) study of the impurity Gd3+ ions in the multi-site SrY2O4 crystal isostructural to the magnetically-frustrated SrGd2O4 compound is reported. Analysis of the angular dependences of the EPR spectra at room temperature allowed us to establish the spin-level energy patterns in the ground states of the Gd3+ ions at the Y(1) and Y(2) sites. Parameters of the spin-Hamiltonian in the frames related to the crystal axes and to the principal center axes are determined.

    更新日期:2018-09-11
  • Electromagnetic modes from Stoner enhancement: Graphene as a case study
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-11
    Z. Jalali-Mola, S.A. Jafari

    In systems with substantial spin fluctuations, dressing the polarization function by ladder diagram of Stoner (spin-flip) excitations can drastically modify the electromagnetic response. As a case study we provide the detailed analysis of the corrections to the non-local optical conductivity of both doped and undoped graphene. While the resummation of ladder diagram of Stoner excitations does not affect the TE mode in doped graphene, it allows for a new undamped TM mode in undoped graphene. This is the sole effect of corrections arising from ladder diagrams and is dominated by Stoner excitations along the ladder rung which goes away by turning off the source of spin-flip interactions. In the case of doped graphene, the inclusion of spin-flip particle-hole fluctuations reduces the energy of plasmon mode.

    更新日期:2018-09-11
  • Long-term stable measurement phantoms for magnetic particle imaging
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-10
    L. Wöckel, J. Wells, O. Kosch, S. Lyer, C. Alexiou, C. Grüttner, F. Wiekhorst, S. Dutz

    Magnetic particle imaging (MPI) is a tomographic imaging method to determine the spatial distribution of magnetic nanoparticles (MNP) within a defined volume. To evaluate the imaging capabilities of existing MPI scanners, their sensitivity and image resolution limits have to be analyzed. Therefore, precisely defined structures (phantoms) with various tracer concentrations are required to enable comparative studies between existing MPI systems. To support the development of capable MPI phantoms, we developed a method to incorporate different commercially available MNP into a long-term stable synthetic polymer with an iron concentration of up to 200 mmol/l. The properties of each type of polymer matrix embedded MNP were tested by magnetic particle spectroscopy (MPS). For shaping the particle loaded polymer to a phantom, we used 3-D printed molds with a structure cross section of 2 x 2 mm2. The particle loads within the phantoms were then imaged using MPI. The particle-loaded polymer is very suitable for preparation of measurement phantoms that could be visualized by MPI. Repeated shore hardness and MPS measurements up to one year did not reveal any changes in the mechanical and magnetic properties of the used material. In conclusion, we developed long-term stable measurement phantoms for magnetic particle imaging. Further work will focus on more detailed particle loaded structures in phantoms and water based polymers with a more homogeneous particle distribution.

    更新日期:2018-09-11
  • Influence of barium and strontium atoms on magnetic properties of iron-containing solid solutions Bi2MNb2O9 (M – Ba, Sr)
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-07
    N.A. Zhuk, N.V. Chezhina, V.A. Belyy, B.A. Makeev, A.S. Miroshnichenko, D.S. Beznosikov, S.V. Nekipelov, V.N. Sivkov, M.V. Yermolina
    更新日期:2018-09-09
  • Influence of cube texture development on magnetic properties of Ni-5at.%W alloy substrates
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-07
    Mangmang Gao, Fangyuan Zhang, Sen Liang, Haibo Li, Lin Ma, Min Liu, Shaheen Kausar, Hongli Suo

    The metallic Ni-5at.%W (Ni5W) substrate with sharp cube texture is found as one of the promising candidates used for fabrication of coated conductors. However, the alternating current (AC) loss, partly contributed by the ferromagnetic Ni5W substrate is unavoidable. In this work, we analyzed the evolution of magnetic properties of Ni5W substrates via the cube texture development. The results revealed that the cube texture has an important impact related to size advantage during recrystallization, leading towards the consumption of the deformation and other orientational grains, and hence giving rise to form a sharp cube texture. Increasing the annealing temperature, the grain size is found to be increased. In the fully developed cube-textured substrate, the grain boundary was replaced by small angle grain boundaries (SAGBs). Also the magnetic domain structure was transformed from 180 °-structure to a branched one with the increasing annealing temperature. This transformation is dependent on the increase of grain size, particularly, the SAGBs plays an important role in the formation of perfect domain structure. Increased coercivity and hysteresis loss in the fully textured substrate can be attributed towards the ideal cube texture and perfect complex domain structure. Therefore, a potential solution has been proposed to resolve this limitation of the sharp cube texture and increased hysteresis loss in Ni5W substrates.

    更新日期:2018-09-09
  • Relaxation time dependencies of optically detected magnetic resonance harmonics in highly sensitive Mx magnetometers
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-08
    M. Ranjbaran, M.M. Tehranchi, S.M. Hamidi, S.M.H. Khalkhali

    Measurement of extremely weak magnetic fields in double-resonance atomic magnetometers based on resonant optical excitation has been an active area of research in recent years. Magnetometer sensitivity can be improved via detection of higher harmonics of the magnetic resonance, a resonance which has a maximum sensitivity under conditions where the ratio of the amplitude to the line-width of the resonance signal is maximized. Based on the Bloch theorem, we analyze the time evolution of the spin polarization corresponding to each harmonic component of the resonance signal and measure this progression experimentally. Our results revealed that there is an optimal harmonic number for achieving the highest sensitivity. We have shown that the longitudinal and transverse relaxation times of spin polarization can manipulate the harmonics with the best sensitivity while the excitation frequency is detuned from the Larmor frequency.

    更新日期:2018-09-09
  • Coupling magneto-elastic Lagrangians to spin transfer torque sources
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-08
    Thomas Nussle, Pascal Thibaudeau, Stam Nicolis

    The consequences of coupling magnetic and elastic degrees of freedom, where spins and deformations are carried by point-like objects subject to local interactions, are studied, theoretically and by detailed numerical simulations. From the constrained Lagrangians we derive consistent equations of motion for the coupled dynamical variables. In order to probe the dynamics of such a system, we consider external perturbations, such as spin transfer torques for the magnetic part, and homogeneous stresses for the elastic part, associated to their corresponding damping. This approach is applied to the study of ultrafast switching processes in anti-ferromagnetic systems, which have recently attracted attention as candidates for anti-ferromagnetic spintronic devices. Our strategy is then checked in simple, but instructive, situations. We carried out numerical experiments to study, in particular, how the magnetostrictive coupling and external stresses affect the nature of the switching processes in a prototype anti-ferromagnetic material.

    更新日期:2018-09-09
  • Boundary structure modification and coercivity enhancement of the Nd-Fe-B magnets with TbCu doping by the process of pre-sintering and hot-pressing
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-08
    Jie Song, Shuai Guo, Guangfei Ding, Kan Chen, Renjie Chen, Don Lee, Aru Yan

    The high-coercivity Nd-Fe-B magnets with “core-shell” structure grains were prepared by doping TbCu powders and hot pressing after pre-sintering in the traditional powder metallurgy process. The coercivity for the hot-pressed pretreated Nd-Fe-B magnet is obviously enhanced to 28.6 kOe from 24.3 kOe by TbCu alloy doping. The Tb contents at the shell structure of grain in the hot-pressed pretreated magnet is 5.7 wt.% while that in the dual-alloy magnet is 3.0 wt.%. The enrichment of Tb elements in the shell layer further enhances the anisotropy of the grain surface and effectively improves the utilization efficiency of heavy rare earths. The existence of the hard (Tb, Nd)2Fe14B shell, which can effectively inhibit the reverse nucleation of magnetic domains, contribute to enhance the coercivity with few reduction of the remanence. Compared with the grain boundary diffusion process, this technology can be used to prepare large pieces of high performance Nd-Fe-B bulk magnets without diffusion depth limit.

    更新日期:2018-09-09
  • Study of structural, morphological and magnetic properties Ag substituted cobalt ferrite nanoparticles prepared by honey assisted combustion method and evaluation of their antibacterial activity
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-08
    M.K. Satheeshkumar, E. Ranjith Kumar, Ch. Srinivas, N. Suriyanarayanan, M. Deepty, C.L. Prajapat, T.V. Chandrasekhar Rao, D.L. Sastry

    Pure and Ag substituted cobalt ferrite nanoparticles (NPs) baring the composition (1–x)CoFe2O4: xAg (x = 0. 0.2) were synthesized by a novel honey assisted combustion method in order to investigate their structural and magnetic properties along withtheir antibacterial activity. XRD patters confirm the spinel phase of CoFe2O4 and the presence of silver (Ag) nanoparticles in the spinel network.The incorporation of Ag in CoFe2O4 spinel structure enhanced the size of the unit cell, resulting to higher value of lattice parameter (a) compared to the pure CoFe2O4. The sintering process promoted the growth of the crystallite sizes (D). The crystallite sizes of the synthesized and annealed powders were found in the range of 24–41 nm. From the EDX studies, it seemed that the distribution of Ag nanoparticles was non-uniform. The saturation magnetization (Ms) and coercivity (Hc) of the powders were influencedbyannealing as well as with the substitution of Ag. The highest value of saturation magnetization (60emu/g) was obtained by the CoFe2O4 nanoparticles with the coercivity value 1358 Oe. The saturation magnetization and coercivity of Ag doped CoFe2O4were less than that of pure CoFe2O4. The present cobalt ferrite nanoparticles and Ag doped cobalt ferrite nanoparticles have showed good antibacterial activities. But Ag doped cobalt ferrite nanoparticles seems to be the potential candidates for affective antibacterial activity. The structural and magnetic results along with the results of antibacterial activities are reportedin the present manuscript.

    更新日期:2018-09-09
  • Alternating Magnetic Field Plate for Enhanced Magnetofection of Iron Oxide Nanoparticle Conjugated Nucleic Acids
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-09-08
    Murat Kaya Yapici, Ahmad Al Nabulsi, Nahla Rizk, Selwa Mokhtar Boularaoui, Nicolas Christoforou, Sungmun Lee
    更新日期:2018-09-09
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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